Glass Stress Measurement Using Fluorescence

ABSTRACT

An apparatus and method for measurement of the stress in and thickness of flat glass or curved glass segments is disclosed that uses fluorescence to quickly and accurately ascertain both the thickness of the stress layers and the wall thickness in addition to the stress curve in flat glass or curved glass segments. The apparatus and method may be used to quickly and accurately measure both the stress in and the thickness of flat glass or curved glass segments at a plurality of various locations therein. The apparatus and method are adapted for large scale flat glass or curved glass segment manufacturing, and are capable of high speed measurement of the stress in and the thickness of the flat glass or curved glass segments.

IDENTIFICATION OF RELATED PATENT APPLICATIONS

This application is related to three other concurrently filed copendingpatent applications, namely U.S. patent application Ser. No. ______,entitled “Glass Container Stress Measurement Using Fluorescence,” U.S.patent application Ser. No. ______, entitled “Glass Container WallThickness Measurement Using Fluorescence,” and U.S. patent applicationSer. No. ______, entitled “Glass Thickness Measurement UsingFluorescence,” all assigned to the assignee of the present patentapplication, which three patent applications are each herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to an apparatus and method formeasurement of the stress across a thickness of glass such as in thewalls of glass containers or in segments of flat glass, and moreparticularly for such an apparatus and method for using fluorescence toquickly and accurately ascertain both the thickness of the stress layersand the wall thickness in addition to the stress curve in glasscontainers or in segments of flat glass.

There are two broad categories of glass that is used in glass containerssuch as bottles, namely “hard” glass and “soft” glass. “Hard” glass,also called borosilicate glass, is made of silica and boron oxide, andrequires much higher temperatures and is more difficult to form, andcosts more than soft glass to manufacture, although it has excellentthermal stress characteristics. “Soft” glass, or soda-lime orsoda-lime-silicate glass, is made of soda, lime, silica, alumina, andsmall quantities of fining agents, and may be manufactured at lowertemperatures and is easier to form and cheaper to manufacture, althoughits thermal stress characteristics are not as good as hard glass. “Soft”glass is the more prevalent type of glass, and it is commonly used forglass containers.

For cost reasons, glass containers today are primarily made of soda-limeglass by molding molten glass into glass containers in blow molds. Asthe container leaves the mold and the glass cools, stress is induced inthe glass, since the outside surfaces of glass containers cooled morerapidly and freeze while the inside surface and the interior walls aremuch hotter and are still flowing. The bottles are then run through anannealing process to remove these stresses.

The assignee of the present patent application has developed a processto thermally strengthen these glass containers. Instead of annealing theglass containers to remove stress, both the outside walls and the insidewalls of the glass containers are rapidly cooled to produce heatstrengthened soda lime glass containers which have intentionallyintroduced stress profiles across the walls of the glass container.There are compressive stresses on both the inside walls and the outsidewalls of the glass container, and tensional stress in the interior ofthe walls of the glass container.

Thermally strengthened soda lime glass containers that have the stresscharacteristics mentioned above are substantially stronger and moredurable, and are much less likely to break when subjected to mechanicalloading or handling or a sudden temperature change. Thus, the improvedstress characteristics that are produced through the use of the improvedcooling technology referenced above result in thermally strengthenedglass containers that have been manufactured from soda lime glass.

While the improved glass container manufacturing technology referencedabove consistently produces thermally strengthened soda lime glasscontainers having excellent stress characteristics, those skilled in theart will at once understand that it is necessary to inspect and verifythe characteristics of the glass containers produced using thistechnology, including the stress characteristics of the glasscontainers. Inspecting the stress characteristics of the wall of athermally strengthened soda lime glass container requires being able tomake a highly accurate determination of the stress throughout thethickness of the wall of each glass container. While various optical andmechanical techniques are well known to locate physical imperfections inglass containers such as small cracks in the glass referred to aschecks, foreign inclusions referred to as stones, bubbles in the glassreferred to as blisters, and excessively thin walls, it is substantiallymore difficult to inspect the stress characteristics of the walls ofglass containers.

Measurement of the stress characteristics of glass containers has beenaccomplished by the inventors using an Immersion light Polariscope(“IP”) that requires the immersion of the glass container beinginspected into a large container of optical index-matched fluid. Such adevice is available from GlasStress Ltd. and is identified as theirAutomatic Transmission Polariscope AP-07. A light source shines aparallel polarized beam through the large container such that the beamtravels tangentially through the side wall of the glass container(passing through the side wall of the glass container), where the beamcrosses the axial stress field inside the side wall of the glasscontainer and change its polarization characteristics as it passesthrough different stress layers across the side wall.

A camera is used to observe the intensity of the polarized component ofthe beam that passes through the side wall of the glass container. Byobserving the intensity of the beam as the polarization of the incomingbeam is rotated, and by taking multiple images for each polarization, adetermination may be made of the stress in the side wall of the glasscontainer. Unfortunately, this Immersion light polariscope techniquerequires a glass container to be immersed in an optical index-matchedfluid, which is not conducive to a large scale manufacturing inspectiontechnique. Additionally, the measurement is not a fast measurement, butinstead is relatively time-intensive, which also makes the techniqueunusable on a large scale manufacturing basis.

Another device available from GlasStress Ltd. is their Scattered LightPolariscope SCALP-03, which performs through-the-thickness stressmeasurement in architectural glass panels and automotive glazing. Thisdevice takes five seconds for a single measurement, works only withlimited glass surfaces, and is inherently unsuitable for application ina mass production environment. The operational theory used by thisdevice is discussed in “A compact Scattered Light Polariscope forResidual Stress Measurement in Glass Plates,” Johan Anton and HillarAben, a poster presented at the Glass Processing Days show in Tampere,Finland, on Jun. 15-18, 2003. To summarize, it uses the scattering of apolarized light beam from a laser as it passes through the glass, androtates this light beam to rotate its polarization to obtain anamplified signal.

It is accordingly desirable to provide an apparatus capable of measuringstress in flat glass or curved glass segments as well as a relatedmethod of measuring the stress in the flat glass or curved glasssegments. It is also desirable that such an apparatus be adaptable forlarge scale flat glass or curved glass manufacturing, such that it wouldbe capable of high speed measurement of the stress in flat glass orcurved glass segments. As such, it desirable that such an apparatus notrequire that the flat glass or curved glass segments be immersed duringthe inspection process, thereby not increasing the difficulty ofhandling of the flat glass or curved glass segments being inspected.

It is further desirable that such an apparatus be capable of producinghighly accurate determinations of the stress in the flat glass or curvedglass segments. It would also be beneficial that such an apparatus becapable of measuring the thickness of each of the stress layers in theflat glass or curved glass segments. In so doing, it would be desirablethat such an apparatus also be capable of measuring the thickness of theflat glass or curved glass segments. Such an apparatus preferably shouldfurther be capable of quickly and accurately measuring both the stressin and the thickness of the flat glass or curved glass segmentsthroughout the entirety of the flat glass or curved glass segments.

Such an improved glass stress measurement apparatus should be of aconstruction which is both durable and long lasting, and it should alsorequire little or no maintenance to be provided by the user throughoutits operating lifetime. In order to enhance the market appeal of such aglass stress measurement system, is should preferably be of relativelyinexpensive construction to thereby afford it the broadest possiblemarket. Finally, it would also be beneficial it all of the aforesaidadvantages and benefits of such a glass stress measurement apparatus andmethod be achieved without incurring any substantial relativedisadvantage.

SUMMARY OF THE INVENTION

The disadvantages and limitations of the background art discussed aboveare overcome by the present invention. With this invention, linearlypolarized light from a laser is coupled into the side wall of a glasscontainer at an optimal angle with respect to the side wall of the glasscontainer in order to obtain an optimum (maximum intensity) fluorescencesignal within the side wall of the glass container. This may beaccomplished by using a right angle isosceles coupling prism (alsoreferred to as a 45 degree-45 degree-90 degree prism) that is opticalglass and is located with the longitudinal axis of its hypotenuse (itslongest side) located tangentially with respect to the side wall of theglass container, and using fluid coupling between the coupling prism andthe outside wall of the glass container. The linearly polarized laserbeam is directed into the coupling prism through one of the shortersides of the coupling prism.

The linearly polarized laser beam thus enters the side wall of the glasscontainer from the outside to the glass container, and, as it enters andpasses through the side wall of the glass container, the linearlypolarized laser beam excites the electronic states of some of theelements and produces fluorescent light along its path. This fluorescentlight source along the path in the side wall of the glass containerallows the stress within the side wall of the glass container to bedetermined. Part of this fluorescent light is linearly polarized on aplane perpendicular to the laser polarization and propagation path.

As this linearly polarized light travels though the stress field in theside wall of the glass container, it changes its polarizationcharacteristics from linear to elliptical to circular to elliptical tolinear, which pattern is repeated. (It should be noted that for typicalwall thicknesses in glass containers the magnitude of the polarizationchange likely never gets all the way to circular polarization. Theapparatus technique of the present invention thus would not need to beable to handle the “wrap around” in signal level that would happenshould it in fact go through circular polarization.) The linearly,circularly, or elliptically polarized fluorescence light exits theoutside wall of the glass container and travels through the couplingfluid to the coupling prism and exits the other of the shorter sides ofthe coupling prism.

The exiting linearly, circularly, or elliptically polarized fluorescencelight that has passed through the stress field in the glass wall is thenconverted to linearly polarized components by a quarter wave plate. Thequarter wave plate is rotated so that the fast axis of the quarter waveplate is aligned with the initial polarization plane (from thefluorescence) of the incident light. The linearly polarized componentsof light then pass through a ferroelectric liquid crystal (“FLC”)rotated at 45 degrees to the quarter wave plate that is alternatelydriven at two different voltages that cause the FLC to alternately passeach component of the fluorescence light.

A camera having a bandpass filter that blocks the laser light and passesfluorescent bandwidths alternately images the linearly polarized lightpassed through the FLC at plus and minus 45 degrees from the axis of thequarter wave plate to produce alternating plus and minus 45 degreeimages having two polar rotations that are 90 degrees apart. Thedifference between alternating images is divided by sum of the twoimages to produce a normalized difference image, which has a line theintensity variation of which is representative of the polarizationchanges from stress effects to the fluorescence light emitted from eachpoint along the laser beam in the side wall of the glass container. (Itshould be noted that if there is no stress, there is no intensityvariation in the difference over sum normalized image.)

By plotting the intensity along this line, a nominally rotated S-shapedretardance curve may be obtained by curve fitting a polynomial which,when differentiated, produces a parabola that is representative of thestress across the thickness of the side wall of a properly thermallystrengthened glass container at the location being tested. In the glassstress measurement system of the present invention, following propercalibration, the length of the light line is proportional to thethickness of the side wall of the glass container. The stress parabolaindicates both the type and magnitude of the stress within the side wallof the glass container, with compression being indicated by a negativevalue in the stress parabola and tension being indicated by a positivevalue in the stress parabola. Accordingly, both the stress within theside wall of a glass container as well as the thickness of side wall ofthe glass container may advantageously be determined using the glassstress measurement system and method of the present invention.

Once calibrated, the glass stress measurement system and method of thepresent invention can quickly determine the stress and the thickness ofthe side wall of a glass container. In an exemplary embodiment, theglass container may be rotated approximately twenty degrees betweenreadings. For this embodiment, the glass container will be rotated totake eighteen readings that are each twenty degrees apart, thereby fullyinspecting the wall thickness and stress of the side wall of the glasscontainer throughout the circumference of the glass container. Glasscontainers not falling within appropriate ranges of wall thickness andstress may be discarded and recycled.

The glass stress measurement system and method of the present inventionis relatively simple to install in the cold end inspection process. Alow volume coupling liquid fluid stream may be supplied to fill thecoupling prism—glass container sidewall interface, with the liquidcoupling fluid being collected by a pan located below the glass stressmeasurement apparatus. The liquid coupling fluid used will be a liquidthat has an index of refraction close to the that of glass; oneacceptable coupling fluid that may be used, for example, is water. Sincethe required readings and rotations may be performed very quickly,implementation of the glass stress measurement system and method of thepresent invention into a high volume glass container manufacturing andinspection line is quite feasible.

Alternatively, light may be coupled into and out of the glass containerusing air as a coupling fluid to fill the coupling prism—glass containersidewall interface. While air may have a coupling efficiency that isless than that of an optimal liquid coupling fluid, it will at once beappreciated by those skilled in the art that the use of air rather thana liquid coupling fluid will present decided advantages in the logisticsof a high speed inspection process in that the entire liquid supply,recovery, and recirculation apparatus is not necessary when using air asthe coupling fluid. This thereby facilitates taking the requiredreadings and rotations very quickly and without wetting the glasscontainers being inspected, thus further enhancing the implementation ofthe glass stress measurement system and method of the present inventioninto a high volume glass container manufacturing and inspection line.

The glass stress measurement system and method of the present inventionis also applicable to measuring the stress distribution across thermallyhardened flat glass or curved glass segments, and is capable of quicklyand accurately measuring both the stress in and the thickness of thewalls of flat glass or curved glass segments. The coupling fluid used tocouple light into and out of flat glass or curved glass segments may beeither a liquid or air. If a liquid is used, it may be applied in a thinlayer to flat glass being inspected or, alternately, sprayed in a lightmist onto the surface of the flat glass or curved glass segments.

It may therefore be seen that the present invention teaches a glassstress measurement system as well as a related method of measuring thestress in flat glass or curved glass segments. The glass stressmeasurement system and method of the present invention are adaptable forlarge scale flat glass or curved glass segment manufacturing, and theyare thus capable of high speed measurement of the stress in flat glassor curved glass segments. The glass stress measurement system and methodof the present invention also do not require that the flat glass orcurved glass segments be immersed in liquid during the inspectionprocess, thereby not increasing the handling of the flat glass or curvedglass segments being inspected.

The glass stress measurement system and method of the present inventionproduce highly accurate determinations of the stress in flat glass orcurved glass segments. The glass stress measurement system and method ofthe present invention are also capable of measuring the thickness ofeach of the stress layers in flat glass or curved glass segments. Theglass stress measurement system and method of the present invention arecapable of measuring the wall thickness of the flat glass or curvedglass segments. The glass stress measurement system and method of thepresent invention are capable of quickly and accurately measuring boththe stress in and the thickness of a plurality of positions in the flatglass or curved glass segments.

The glass stress measurement system of the present invention is of aconstruction which is both durable and long lasting, and it should alsorequire little or no maintenance to be provided by the user throughoutits operating lifetime. The glass stress measurement system of thepresent invention is also be of relatively inexpensive construction toenhance its market appeal and to thereby afford it the broadest possiblemarket. Finally, the glass stress measurement system and method of thepresent invention achieves all of the aforesaid advantages andobjectives without incurring any substantial relative disadvantage.

DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention are best understoodwith reference to the drawings, in which:

FIG. 1 is an isometric depiction of the lower half of a glass containerschematically illustrating a three dimensional coordinate system withinthe glass container for discussing the stress field;

FIG. 2 is a light intensity curve analysis result related to theretardance in the path of the polarized light, located above a stressparabola, with both curves being plotted against the thickness of a sidewall in a glass container having an optimal stress parabola;

FIG. 3 is a diagram illustrating in highly schematic form the glassstress measurement system of the present invention;

FIG. 4 is an isometric view of the essential components of the glassstress measurement system of the present invention illustrated in FIG. 3being used to evaluate the wall of a glass container, with an optionalprism being used to make the apparatus more compact;

FIG. 5 is a plan view of the apparatus and glass container illustratedin FIG. 4 from the top thereof, also schematically showing apparatusused to rotate the glass container;

FIG. 6 is an elevation view of the apparatus and glass containerillustrated in FIGS. 4 and 5 from the side thereof in the horizontalplane of the entry of the light beam into the side wall of the glasscontainer;

FIG. 7 is an isometric view of the apparatus and glass containerillustrated in FIGS. 4 through 6 located in mounting apparatus used tosupport the various components adjacent a starwheel glass containerapparatus, also showing a coupling fluid distribution system used toprovide fluid coupling of the light into and out of the glass container;

FIG. 8 is an isometric view of the apparatus illustrated in FIG. 7,showing an adjustable support mechanism for the apparatus;

FIG. 9 is a is an isometric view of the apparatus illustrated in FIG. 8,with the various housing elements removed for clarity, together with aglass container being tested;

FIG. 10 is a first image taking by the camera at a first of the twoalternating images having a first polar rotation;

FIG. 11 is a second image taking by the camera at a second of the twoalternating images having a second polar rotation orthogonal to thefirst polar rotation;

FIG. 12 is a normalized difference image taken by subtracting the secondimage illustrated in FIG. 11 from the first image illustrated in FIG.10;

FIG. 13 is a display showing the line intensity of the portion of thenormalized difference image shown in FIG. 12 plotted along the length ofwall of the glass container, together with other information depicted aswell in the display;

FIG. 14 is a flowchart showing the method used by the exemplaryembodiment to measure glass stress and wall thickness; and

FIG. 15 is an isometric view of the essential components of the glassstress measurement system of the present invention illustrated in FIG. 3being used to evaluate the thickness of a segment of flat glass, with acoupling prism being used to make the apparatus more compact and acoupling fluid being located on the surface of the segment of flat glassto provide fluid coupling of the light into and out of the segment offlat glass.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Prior to discussing exemplary embodiments of the glass stressmeasurement system and method of the present invention, a briefdiscussion of some of the principles used by the present invention willbe provided. Referring first to FIG. 1, a coordinate system for threedimensional stress in a glass container 30 (the lower portion of whichis illustrated in FIG. 1) is provided. Radial stress is defined acrossthe wall of the glass container 30, in a first of three relativelyorthogonal directions. Hoop stress is defined around the circumferenceof the glass container 30, in a second of the three relativelyorthogonal directions. Axial stress is defined along the height of theglass container 30, in a third of the three relatively orthogonaldirections.

The thermal strengthening of the glass container 30 in rapidly cools theinner and outer surfaces of the glass container 30 until the inner andouter surface temperatures are below the glass transition temperature,thereby freezing the surface structure of the glass container 30 whileallowing the inner glass to continue to flow until its temperaturereaches the glass transition temperature, then letting the glasscontainer 30 cool to room temperature. This process enhances the stresscharacteristics of the glass container 30, making it substantiallystronger and more durable. When the container reaches room temperature,the inner and outer surfaces of the glass container 30 will be incompression and the interior of the walls of the glass container 30 willbe in tension. In a properly controlled cooling process, the magnitudeof the hoop stress and the axial stress at the surface of the glasscontainer 30 (and indeed at any point across the thickness of the wallsof the glass container 30) should be nearly equal. The stress along thethickness of the walls of the glass container 30 should thus vary fromcompression at the outer walls to tension in the interior of the wallsto compression at the inner walls, with very little or no net radialstress.

The glass stress measurement system and method of the present inventionuses the fluorescent light produced by a laser beam passing through thewall of a glass container as a linear polarized light source in order todetermine the stress in the wall of the glass container. As polarizedlight passes through stressed glass, the phase of the light will changeas it goes through the stress field. Linearly polarized fluorescentlight emitted from along the entire laser beam path inside of the wallof a glass container will become elliptically or circularly polarized asit pass through the stressed wall of the glass container.

The glass stress measurement system and method of the present inventionuses the optical principle that normally transparent isotropicsubstances are made optically anisotropic by the existence of internalstresses therein. This phenomenon, known as stress birefringence, existsas the difference in refractive index between two orthogonally polarizedmodes, and will vary from point to point throughout the wall of a glasscontainer as the stress in the wall of the glass container varies.Retardance is the difference in optical path length between the twoorthogonally polarized modes, and the present invention will determinethe retardance along the light path within the wall of a glass containerfrom the intensity of the emitted fluorescent light from along theentire laser beam path within the wall of the glass container in the twoorthogonally polarized modes.

The viewing angle and the angle of polarization being emitted from thefluorescence are chosen to maximize the difference between the twoorthogonally polarized modes being evaluated within the constraints ofthe improvements described. Referring back to FIG. 1 for the moment, byviewing at 45 degrees to a tangent of the hoop (the circumference of theglass container 30), the axial stress is fully acting in the verticaldirection, but that angle means that the horizontal direction would be apartial combination of Hoop and Radial. Because of refraction effectsdiscussed earlier, the angle can not be decreased to look tangentiallyas in the immersion polariscope.

Referring next to FIG. 2, two curves are shown, with the top curve beinga plot of the retardance curve from an outside wall 32 to a midpoint ofthe wall 34 to an inside wall 36 of a glass container having an idealstress distribution throughout its wall. Located below the retardancecurve is a parabola having values that are the derivative of the valuesof the retardance curve. This parabolic curve is the stress parabola,and is a calculated plot of the stress from the outside wall 32 to theinside wall 36 of the glass container, and has an ideal stressdistribution throughout its wall varying from compression at the outerwall 32 to tension in the interior of the wall (including the midpointof the wall 34) to compression at the inside wall 36. Glass containersnot having the proper characteristics are unacceptable, and the glassstress measurement system and method of the present invention isdesigned to evaluate glass containers and determine the stress parabolain order to identify glass containers not having proper stresscharacteristics so that they may be discarded.

Referring now to FIG. 3, an exemplary embodiment of the glass stressmeasurement system of the present invention is shown in highly schematicfashion with respect to a glass container 30. (It will be understood bythose skilled in the art that the principles of operation demonstratedwith respect to the example using the glass container 30 shown in FIG. 3are equally applicable to flat glass or curved glass.) A laser lightsource 40 produces a linearly polarized light beam 42 that is coupledinto the outside wall 32 of the glass container 30 at an optimal angle(to be discussed below). The laser light source 40 is either mounted ina manner permitting its rotation to rotate the polarization of thelinearly polarized light beam, or, alternately, an optional half waveplate 44 may be used between the laser light source 40 and the outsidewall 32 of the glass container 30 to rotate the polarization of thelinearly polarized light beam 42 to the desired orientation. Thispolarization direction will be in a plane that is parallel to a planethat is orthogonal to the axis of fluorescent light exiting the sidewall of the glass container 30 toward the CCD camera 60.

The linearly polarized light beam 42 refracts and enters into the sideof the glass container 30, where it is depicted as a refracted lightbeam 46 that will repeatedly change its polarization characteristicsfrom linearly polarized to elliptically polarized to circularlypolarized to elliptically polarized and back to linearly polarized as itpasses through the stress field and will generate fluorescent light 48that will have a polarization dependent component at each point alongthe light beam 42 in the side wall of the glass container 30. Thepolarization of the fluorescent light 48 orthogonal to the laser beam 46will be primarily linear polarized, but with a fixed intensity variationattributed to the stress experienced while entering the glass plus arange of other things, including the color of the glass.

The emitted linearly polarized fluorescent light 48 from the laser beam46 is affected by the stress induced retardance along the exit path suchthat the fluorescent light 48 represents just one specific ray from nearthe center of the container wall thickness. It is important to note thatthe light beam 46 will generate fluorescent light along its length, andthat line of fluorescent light, of which the fluorescent light 48represents one ray, will exit the glass container 30 through the outsidewall 32, where it will constitute the line light to be imaged, of whichthe light beam 50 represents one ray.

A quarter wave plate 52 mounted at an appropriate angle is used toconvert the elliptically polarized components of the light beam 50 intolinearly polarized light to allow an evaluation of how much of thelinearly polarized fluorescent light 48 became circularly orelliptically polarized. The orientation of the axis of the quarter waveplate 52 will be at an angle that is aligned with respect to thelinearly polarized light radiating from the fluorescence along the lightbeam 46. A polarization rotator 54 is used to modulate the state of thepolarization state of the now linearly polarized light beam 50 plus andminus 45 degrees with respect to the axis of the quarter wave plate 52,which itself is also at an angle of 45 degrees with respect to thelinearly polarized light radiating from the fluorescence along the lightbeam 46. The polarization rotator 54 is a ferroelectric liquid crystal(“FLC”) element that is driven by alternating positive and negativevoltages from a rotator drive 56.

The thusly modulated linearly polarized light beam 50 then passesthrough a long pass filter 58 that passes fluorescent light (andpreferably does not pass light at the frequency of the linearlypolarized light beam 42), with the fluorescent portion of the linearlypolarized light beam 50 being viewed by a CCD camera 60. Alternately, abandpass filter or a notch filter could be used instead of the long passfilter 58. Alternating images are produced by the CCD camera 60 with thealternating positive and negative voltages produced by the rotator drive56 driving the polarization rotator 54. These alternating images areacquired from the CCD camera 60 by an image acquisition module 62, andare schematically depicted as a first image 64 that is produced when therotator drive 56 supplies a positive voltage to the polarization rotator54, and a second image 66 that is produced when the rotator drive 56supplies a negative voltage to the polarization rotator 54. (Thoseskilled in the art will appreciate that the alternating images producedare of different polarization analysis states, and the alternating couldinstead be produced by other apparatus, such as, for example, by usingtwo sensors with a polarizing beam splitter.)

These two images 64 and 66 are processed by subtracting the second image66 from the first image 64 and dividing by the sum of the two images 64and 66, with a normalized difference image 68 being produced. Byprocessing the normalized difference image 68 in an image analysismodule 70, a retardance curve and a stress parabola similar to thoseillustrated in FIG. 2 may be derived, and by processing this data thethickness of each of the stress layers in the wall of a glass containeras well as the thickness of the wall itself may also be derived. Thisanalysis will be discussed in more detail in conjunction with FIG. 13.

It should be noted that in order to obtain the thickness of the wallitself and/or the thickness of each of the stress layers in the wall ofa glass container, it is not necessary to use the normalized differenceimage 68. Instead, by processing the data from either of the images 64and 66, the thickness of the wall itself and the thickness of each ofthe stress layers in the wall of a glass container may be derivedwithout use of the normalized difference image 68. Further, if only thethickness of the wall itself and the thickness of each of the stresslayers in the wall are being measured, the apparatus shown in FIG. 3would not need the quarter wave plate 52 or the polarization rotator 54.Instead, the CCD camera 60 would acquire a single image through the longpass filter 58 of the polarized components of the light beam 50 emittedfrom the glass container 30.

Referring next to FIGS. 4 through 6, the system that is schematicallyillustrated in FIG. 3 with respect to the glass container 30 isillustrated in an exemplary embodiment omitting for clarity a housingmember that will be used to maintain the relative locations of thevarious components and their optical paths respectively fixed in theirpreferred locations (this housing member which is unseen in FIGS. 4through 6 is depicted in FIG. 7 as a component identified by thereference numeral 100) Wherever possible, the reference numbers used inFIG. 3 are also used in FIGS. 4 through 6.

It should be noted that the glass stress measurement system and methodof the present invention shown in FIGS. 4 through 6 is geometricallydesigned to use water (which has an index of refraction close to thethat of glass) as a coupling fluid to couple light into and out of theglass container 30, while the alternate use of air as coupling fluidwould necessitate different geometry to optimize the coupling of lightinto and out of the glass container 30. Thus, those skilled in the artwill appreciate that the optimal angles of entry into and exit from theglass container 30 will be different for different coupling fluids.

The light beam used for the analysis is generated by the laser lightsource 40. In the exemplary embodiment, the laser light source 40 may bea diode laser in any of a variety of different colors, including, forexample, green, blue, and red. The particular color of the laser lightto be used may be selected based upon the characteristics of the glasscontainer to be inspected. For example, a red laser is believed to bebest with amber glass containers since amber glass absorbs green andblue light. A green laser is believed to be best for flint colorlessglass containers, and a blue laser is believed to be best with bluishcolor glass containers. An exemplary setup for use in analyzing clearcolorless glass containers may use a green laser.

The laser light selection criteria used should include the fact thatfluorescent light has a longer wavelength than the light that is used tocreate it. Accordingly, the selection of the laser light source 40should be made to make it easy to observe the fluorescent lightgenerated in the wall of the glass container 30. Thus, deep red will beproduced from a red laser beam, green to red will be produced from ablue laser beam, and yellow to deep red will be produced from a greenlaser beam. The excitation wavelength may also be chosen by themagnitude of the nearly linear polarization in the emitted fluorescence.

The laser light source 40 generates a linearly polarized laser lightbeam 42 of an appropriately selected wavelength that will be coupledinto the side wall of the glass container 30. The linearly polarizedlight beam 42 is oriented with a polarization direction that is selectedto produce an optimal (the largest possible magnitude) fluorescentsignal intensity of the light beam 50 exiting the side wall of the glasscontainer 30. This polarization direction will be in a plane that isparallel to a plane that is orthogonal to the axis of fluorescent lightexiting the side wall of the glass container 30. While in the exemplaryembodiment the half wave plate 44 shown in phantom lines may be used torotate the polarization of the linearly polarized light beam 42 to thedesired orientation, it may be easier to mount the laser light source 40such that it may be rotated to rotate the polarization of the linearlypolarized light beam 42 to the desired orientation.

The linearly polarized light beam 42 is coupled into the glass container30 in the exemplary embodiment illustrated in FIGS. 4 though 6 using aright angle isosceles coupling prism 80 that is oriented with itshypotenuse located tangentially (and with its triangular surfaces inhorizontal planes) with respect to the side wall of the glass container.As mentioned above, the embodiment illustrated in FIGS. 4 through 6 isgeometrically designed to use water as the coupling fluid between thecoupling prism 80 and the outside wall of the glass container 30. Thelaser light source 40 is mounted such that the linearly polarized lightbeam 42 will enter one of the shorter sides of the coupling prism 80 ata downwardly oriented angle of approximately 45 degrees from ahorizontal plane (which plane is orthogonal to the axis of the glasscontainer 30).

For the water-coupled embodiment being discussed, this will orient thelinearly polarized light beam 42 such that it enters the side wall ofthe glass container 30 at an angle of approximately 45 degrees from thenormal to the surface of the glass container 30 at the point of entrywhen viewed from directly above (this angle being in the horizontalplane orthogonal to the axis of the glass container 30), and at a 45degree angle from the horizontal plane orthogonal to the axis of theglass container 30. This approximate angle of entry is selected tomaximize the linear polarization and signal.

This results in a compound angle at the surface of the glass container30 of 60 degrees from the normal to the surface. Since the index ofrefraction for water is 1.333 and the approximate index of refractionfor the material of the glass container 30 is 1.51, the resulting anglein the wall of the glass container 30 will be approximately 40.51degrees from the normal. Due to the curvature of the glass container 30,the relative positioning of the glass container 30, and variations inthe glass container 30 due to production tolerances, this angle willvary slightly.

Thus, the light beam 46 is oriented inside the glass of the side wall ofthe glass container 30 in order to provide optimum signal levels. Inthis configuration, the axial stress is entirely affecting the verticalcomponent of the 45 degree angle polarization, and only a portion of thehoop stress, combined with the nearly zero radial stress, are affectingthe horizontal component of the 45 degree polarization. At other anglesof orientation of the fluorescent light 48 from the fluorescence fromthe light beam 46, contribution by axial and hoop stress will varyaccording to the component of the stress field that the polarized lightbeam 42 crosses.

This geometric relationship is selected for a water-coupled embodimentto put the fluorescence from the light beam 46 in the focus plane of theCCD camera 60 and the right angle (orthogonal) relationship between theexciting linearly polarized light beam 42 and the viewing anglemaximizes the linear polarization and signal, and also since the use ofa smaller angle results in a small signal.

The location from which the fluorescent light generated from the lightbeam 42 inside the side wall of the glass container 30 is observed isorthogonal to the other of the shorter sides of the coupling prism 80,with the light beam 50 being oriented in the horizontal plane at anangle of approximately 45 degrees from the normal to the surface of theglass container 30. The light beam 50 is thus the result of thefluorescence whose linear polarization component is at 45 degrees tohorizontal, and has been affected by the stress field along the pathfrom the fluorescence source along the light beam 46 to its exit fromthe glass container 30.

The light beam 50 then passes through the quarter wave plate 52 and thepolarization rotator 54. For purposes of convenience in mounting thevarious components of the glass stress measurement apparatus of thepresent invention in a compact configuration, a bending prism 82 is usedto bend the light beam 50 at a 90 degree angle. The bending prism 82 isalso a right angle isosceles prism.

After passing through the quarter wave plate 52 and the polarizationrotator 54, the light beam 50 is bent in the bending prism 82, and thenpasses through the long pass filter 58, which is mounted on a lens 84 ofthe CCD camera 60. The orientation of the axis of the quarter wave plate52 would be at an angle that is aligned with respect to the linearlypolarized light from the fluorescence within the glass container 30,ignoring the presence of the bending prism 82 and assuming that thequarter wave plate 52 was mounted parallel to the other of the shortersides of the coupling prism 80.

The quarter wave plate 52 may be selected by doing a fluorimeter plot ofintensity as it varies by wavelength, and using the wavelength of thehighest intensity point of the plot to select the appropriate thequarter wave plate 52. For example, if the highest intensity point is at700 nanometers, a 175 nanometer quarter wave plate 52 would be selected.The appropriate polarization rotator 54 may be selected in similarfashion.

The lens 84 may have an aperture that is wide open to allow more lightto reach the CCD camera 60, since virtually no depth of focus isnecessary to view the light beam 42 as it passes through the side wallof the glass container 30 in a plane that extends downwardly atapproximately 45 degrees. The fluorescent light that generates the lightbeam 50 extends orthogonally out of that focal plane and may thus becaptured by the CCD camera 60. Thus the line of view captured by the CCDcamera 60 is at 45 degrees from a plane tangential to the side wall ofthe glass container 30, and in the horizontal plane.

Also shown in FIGS. 5 and 6 in phantom lines is apparatus for rotatingthe glass container 30 in order to allow the apparatus of the presentinvention to measure the stress in the side wall of the glass container30 as well as its thickness at a plurality of angular positions as theglass container 30 is rotated. One side of the glass container 30 issupported for rotation near its bottom by a pair of rollers 86 and 88and near its top by a pair of rollers 90 and 92. A drive roller 94 isused to rotate the glass container 30, which is supported on a deadplate96. In the exemplary embodiment, the stresses and the thickness of theside wall of the glass container 30 will be evaluated at approximately20 degree angular increments, which has been found to be a sufficientsampling in order to fully evaluate the stresses and the thickness ofthe side wall of the glass container 30.

Prior to further elaborating on the implementation of the water-coupledembodiment, the geometry for an air-coupled embodiment may first bediscussed. At present, it is believed that the optimal geometry for anair-coupled embodiment would orient the linearly polarized light beam 42such that it enters the side wall of the glass container 30 at an angleof approximately 60 degrees from the normal to the surface of the glasscontainer 30 at the point of entry when viewed from directly above (thisangle being in the horizontal plane orthogonal to the axis of the glasscontainer 30), and at a 45 degree angle from the horizontal planeorthogonal to the axis of the glass container 30. This approximate angleis selected for an air-coupled embodiment to maximize the linearpolarization and signal.

This would result in a compound angle at the surface of the glasscontainer 30 of 69.29 degrees from the normal to the surface. Since theindex of refraction for air is 1.0 and the approximate index ofrefraction for the material of the glass container 30 is 1.51, theresulting angle in the wall of the glass container 30 will beapproximately 38.278 degrees from the normal. Due to the curvature ofthe glass container 30, the relative positioning of the glass container30, and variations in the glass container 30 due to productiontolerances, this angle would vary slightly.

The location from which the fluorescent light generated from the lightbeam 42 inside the side wall of the glass container 30 is air-coupledout of the glass container 30 would provide the light beam 50 at anorientation in the horizontal plane at an angle of approximately 60degrees from the normal to the surface of the glass container 30. Theseapproximate angles of entry into and exit from the glass container areselected to maximize the signal detected (the light beam 50 emitted fromthe glass container 30).

In general, and for a wide variety of potential coupling fluids, thepreferred orientations of the glass stress measurement system and methodof the present invention appear to be angles of between approximately 40degrees and approximately seventy from the normal to the surface of theglass container 30 at the point of entry when viewed from directlyabove, with a 45 degree angle from the horizontal plane orthogonal tothe axis of the glass container 30.

Referring now to FIG. 7, the installation of the apparatus of FIGS. 4through 6 into a production environment using water as a coupling fluidis illustrated. The laser light source 40 and the CCD camera 60 areshown mounted into a machine head housing 100. The coupling prism 80,the bending prism 82, the quarter wave plate 52, and the polarizationrotator 54 are mounted inside the machine head housing 100 in theorientation in which they are shown in FIGS. 4 through 6. The machinehead housing 100 is mounted on a support arm, indicated generally by thereference numeral 102, which in turn is mounted on a support column 104.

As mentioned above, fluid coupling is used to couple the light betweenthe coupling prism 80 and the side wall of the glass container 30. Inthis exemplary embodiment, water is used as the coupling fluid, since ithas an index of refraction that is close to that of glass. The water isdelivered to a point just above the interface between the coupling prism80 and the side wall of the glass container 30 by a nozzle 106. Thewater is delivered from a fluid source 108 such as a pump through avalve 110 to the nozzle 106.

The water is collected from under the machine head housing 100 at theunderside of the interface between the coupling prism 80 and the sidewall of the glass container 30 by a vacuum tube 112. A fluid vacuum 114is connected to the vacuum tube 112 to collect the water, and returns itto the fluid source 108 for reuse. If desired, a filter may be insertedbetween the fluid vacuum 114 and the fluid source 108 to cleanimpurities from the water prior to supplying it to the fluid source 108.

Referring briefly to FIGS. 8 and 9, the apparatus of the presentinvention is shown as it is mounted on the underside of the support arm102. Referring specifically to FIG. 9, it may be seen that the supportarm 102 may be of two-piece construction, thereby allowing for anotherdegree of adjustment. A distal portion 116 of the support arm 102 ispivotally mounted on a proximal portion 118 of the support arm 102. Thiscapability for adjustment, together with the ability to adjust theheight of the support arm 102 on the support column 104, allows for theapparatus of the present invention to be adjusted to accommodatevirtually any manufacturing line configuration.

As mentioned above in conjunction with FIG. 3, two alternating images 64and 66 are captured by the CCD camera 60. Exemplary such images 64 and66 are respectively shown in FIGS. 10 and 11. The first image 64 shownin FIG. 10 is produced when the rotator drive 56 supplies a positivevoltage to the polarization rotator 54, and the second image 66 shown inFIG. 11 is produced when the rotator drive 56 supplies a negativevoltage to the polarization rotator 54.

Referring to the first image 64, an image that resembles a cross layingsideways with the crossbar of the cross being rotated counterclockwisefrom an orthogonal position is visible. The lower portion of the leg ofthe cross 120 extends from left to right, with the upper portion of legof the cross 122 extending further to the right of the lower portion ofthe cross. A first side of the crossbar 124 extends from theintersection of the lower portion of the leg of the cross 120 and theupper portion of the leg of the cross 122 upwardly and leftwardly, and asecond side of the crossbar 126 extends from the intersection of thelower portion of the leg of the cross 120 and the upper portion of theleg of the cross 122 downwardly and rightwardly. At the intersection ofthe leg of the cross and the crossbar of the cross is an intersectionpoint of the cross 128.

The horizontal lower portion of the leg of the cross 120 is thefluorescent portion of the modulated linearly polarized light beam 50that shows the fluorescence from the light beam 46 (shown in FIG. 3)inside the side wall of the glass container 30, which terminates in thebright spot at the intersection point of the cross 128 which is theinner wall of the glass container 30. The first side of the crossbar 124is the reflection of the light beam 42 from the inner wall of the glasscontainer 30, and the second side of the crossbar 126 from theintersection point of the cross 128 is the light beam 42 hitting theinner wall of the glass container 30 and being reflected downwardly intothe glass of the side wall of the glass container 30 and producesfluorescent light along that path. The upper portion of the leg of thecross 122 is a reflection of the downwardly reflected light beam 46 inthe glass represented by the second side of the crossbar 126.

Referring now to the second image 66, a similar cross-shaped imagelaying sideways with its crossbar being rotated counterclockwise from anorthogonal position is visible. The horizontal lower portion of the legof the cross 130 extends from left to right, with the upper portion ofleg of the cross 132 extending further to the right of the lower portionof the cross. A first side of the crossbar 134 extends from theintersection of the lower portion of the leg of the cross 130 and theupper portion of the leg of the cross 132 upwardly and leftwardly, and asecond side of the crossbar 136 extends from the intersection of thelower portion of the leg of the cross 130 and the upper portion of theleg of the cross 132 downwardly and rightwardly. At the intersection ofthe leg of the cross and the crossbar of the cross is an intersectionpoint of the cross 138.

As is the case in the first image 64, the horizontal lower portion ofthe leg of the cross 130 is the fluorescent portion of the modulatedlinearly polarized light beam 50 that shows fluorescence from the lightbeam 46 inside the side wall of the glass container 30, which terminatesin the bright spot at the intersection point of the cross 138 which isthe inner wall of the glass container 30. The first side of the crossbar134 is the reflection of the light beam 46 from the inner wall of theglass container 30, and the second side of the crossbar 136 from theintersection point of the cross 138 is the light beam 42 hitting theinner wall of the glass container 30 and being reflected downwardly inthe glass of the side wall of the glass container 30 and producesfluorescence along that path. The horizontal upper portion of the leg ofthe cross 132 is a reflection of the downwardly reflected light beam 46in the glass represented by the second side of the crossbar 136. Thelocation of the side wall of the glass container 30 is shown by a line140 representing the thickness of the side wall of the glass container30 that is drawn onto the second image 66 by the system to betteridentify the location of the side wall of the glass container 30. Itshould be noted that by processing the data from the second image 66,the thickness of the wall itself (shown by the line 140) and thethickness of each of the stress layers in the wall of a glass containermay be derived. This information could also be derived from the firstimage 64 shown in FIG. 10.

Referring next to FIG. 12, a normalized difference image 68 is shownthat is generated by subtracting the second image 66 illustrated in FIG.11 from the first image 64 illustrated in FIG. 10 and dividing by thesum of first image 64 and second image 66. The normalized differenceimage 68 shows a somewhat different cross-shaped image laying sidewayswith its crossbar being rotated counterclockwise from an orthogonalposition is visible. The lower portion of the leg of the cross 150extends from left to right, with the upper portion of leg of the cross152 extending further to the right of the lower portion of the cross. Afirst side of the crossbar 154 extends from the intersection of thelower portion of the leg of the cross 150 and the upper portion of theleg of the cross 152 upwardly and leftwardly, and a second side of thecrossbar 156 extends from the intersection of the lower portion of theleg of the cross 150 and the upper portion of the leg of the cross 152downwardly and rightwardly. At the intersection of the leg of the crossand the crossbar of the cross is an intersection point of the cross 158.

Once again, the horizontal lower portion of the leg of the cross 150 isthe fluorescent portion of the modulated linearly polarized light beam50 that shows fluorescence from the light beam 46 inside the side wallof the glass container 30, which terminates in the bright spot at theintersection point of the cross 158 which is the inner wall of the glasscontainer 30. The first side of the crossbar 154 is the reflection ofthe light beam 46 from the inner wall of the glass container 30, and thesecond side of the crossbar 156 from the intersection point of the cross158 is the light beam 42 hitting the inner wall of the glass container30 and being reflected downwardly in the glass of the side wall of theglass container 30. The upper portion of the leg of the cross 152 is areflection of the downwardly reflected light beam 42 in the glassrepresented by the second side of the crossbar 156. The location of theside wall of the glass container 30 is shown by a line 160 representingthe thickness of the side wall of the glass container 30 that is drawnonto the second image 66 by the system to better identify the locationof the side wall of the glass container 30.

By processing the normalized difference image 68 of FIG. 12 in the imageanalysis module 70 (shown in FIG. 3), a glass stress display retardancecurve 170 as shown in FIG. 13 may be generated. By plotting theintensity of the horizontal lower portion of the leg of the cross 150 ofthe normalized difference image 68 (shown in FIG. 12) along the line 160representing the thickness of the side wall of the glass container 30(also shown in FIG. 12), a jagged nominally S-shaped curve 172 may beobtained. A polynomial best fit S-shaped curve 174 is generated from therotated jagged nominally S-shaped curve 172, and represents theretardance curve of the side wall of the glass container 30.

The polynomial best fit S-shaped curve 174 is then differentiated by thesystem to produce a parabola 176 that is representative of the stressthroughout the side wall of the glass container 30 at the location beingtested. The system may also automatically determine the maximum andminimum locations in the polynomial best fit S-shaped curve 174, andthese locations may be automatically displayed as a maximum trace 178having a peak at the location determined to be the maximum of thepolynomial best fit S-shaped curve 174 and as a minimum trace 180 havinga peak at the location determined to be the minimum of the polynomialbest fit S-shaped curve 174.

By further processing the data used to provide the glass stress display170, the thickness of each of the stress layers in the wall of a glasscontainer as well as the thickness of the wall itself may be derived. Ifdesired, these calculations could also be shown on the glass stressdisplay 170, although they are not so shown in FIG. 13. (As mentionedabove, both the thickness of the wall and the thickness of each of thestress layers in the wall could also be derived from the first image 64or the second image 66 instead.)

Referring next to FIG. 14, the method practiced by the exemplaryembodiment of the present invention is illustrated. A production line isused to successively bring each of a plurality of the glass containers30 into position for inspection by the apparatus of the presentinvention. The glass container 30 in position for inspection is rotatedby a rotating mechanism 190 so that the side wall of the glass container30 may be inspected by the apparatus of the present invention at aplurality of angular locations. In the exemplary embodiment discussedherein, the glass container 30 inspection of the side walls of the glasscontainer 30 will be taken approximately every 20 degrees, with theglass container 30 being rotated to take 18 successive readings that areeach 20 degrees apart, thereby fully allowing the stress of the sidewall of the glass container 30 and the wall thickness of the glasscontainer 30 to be fully inspected.

A coupling fluid source 192, which may include the fluid source 108,111, and the nozzle 106 (all of which are shown in FIG. 7), provides acoupling fluid 194, which as discussed above may be water, to a locationbetween the coupling prism 80 and the side wall of the glass container30. The coupling fluid is collected by a coupling fluid collector 196,which may include the vacuum tube 112 and the fluid vacuum 114 (whichare also shown in FIG. 7) The coupling fluid may be filtered andreturned to the coupling fluid source 192.

A linearly polarized light beam 42 is provided by the laser light source40 and is coupled into the side wall of the glass container 30 throughthe coupling prism 80. The laser light source 40 may be mounted in amanner permitting it to be rotated as indicated by the reference numeral198 to thereby rotate the polarization of the linearly polarized lightbeam 42 slightly to maximize the output signal from the system.Alternately, the half wave plate 44 may be placed between the laserlight source 40 and the coupling prism 80, with the half wave plate 44being rotated as indicated by the reference numeral 198 to therebyrotate the polarization of the linearly polarized light beam 42 slightlyto maximize the output signal from the system.

The linearly polarized light beam 42 passes through the coupling prism80 and the coupling fluid 194, and then enters into the side wall of theglass container 30, where it will generate fluorescent light have bothlinearly polarized and unpolarized components that will be affected bythe stress state in the glass in its path to exit the side wall of theglass container 30 as the light beam 50. The light beam 50 is coupledfrom the side wall of the glass container 30 through the coupling prism80. It passes through the quarter wave plate 52, which may be rotated asindicated by the reference numeral 202 to thereby optimize theconversion of the linearly polarized and elliptical components of thelight beam 50 into linearly polarized light.

The linearly polarized light beam 50 is then passed through thepolarization rotator 54, which is operated as indicated by the referencenumeral 204 to produce alternating images having polar rotations each 45degrees from the axis of the quarter wave plate 52. The alternatingimages from the linearly polarized light beam 50 may optionally bereoriented by the bending prism 82, following which they pass throughthe long pass filter 58 to filter out non-fluorescent frequencies.

The CCD camera 60 produces alternating images corresponding to thealternation of the polarization rotator 54, which alternating images areprocessed into a normalized difference image 68 in an imagedifferentiator 206. The normalized difference image 68 is provided to animage processor 208 which processes the information from the normalizeddifference image 68 and provides the processed information to systemlogic 210. The system logic 210 provides as an output thecharacteristics 212 of the side wall of the glass container 30 that wasinspected, which include the normalized difference image 68 which,together with other information, may be displayed in a display glasscontainer information step 214. Following determination of thecharacteristics 212 of the side wall of the glass container 30 that wasinspected at each of the angular positions for the glass container 30, adetermination 216 may be made as to whether to keep or discard the glasscontainer 30. Glass containers the glass container 30 not falling withinappropriate ranges of wall thickness and stress may be discarded andrecycled.

Referring finally to FIG. 15, the use of the glass stress measurementsystem of the present invention for measuring the stress in a segment offlat glass 220 is illustrated. The segment of flat glass 220 has acoupling fluid 222 which in the exemplary embodiment shown in FIG. 15may be water, since water has an index of refraction that is close tothat of glass than that of air. The segment of flat glass 220 may belocated in a container 224 in order to confine a thin film of thecoupling fluid 222 on the surface of the segment of flat glass 220.

Alternately, a coupling fluid supply and recycling system similar infunction to the one illustrated in and discussed in conjunction withFIG. 7 above may be used to provide the coupling fluid 222 only in thearea of the segment of flat glass 220 being measured may be utilized.Still another way using a liquid coupling agent would be to spray a thinfilm of the liquid coupling agent on the flat glass 220 immediatelyahead of the movement thereto of the apparatus illustrated in FIG. 15.Further, (If a curved segment of glass is being evaluated, the sprayingtechnique may prove to be particularly useful, since placing a thin filmof coupling fluid on a curved segment of glass would be impractical.)

However, it may also be appreciated by those skilled in the art that theuse of air coupling would be even more beneficial.

The optical system shown in and discussed in conjunction with FIGS. 4through 6 above is shown and utilized in FIG. 15, with the couplingprism 80 having its hypotenuse located parallel to and close adjacent tothe top side of the segment of flat glass 220 with a thin film of thecoupling fluid 222 located between the coupling prism 80 and the topside of the segment of the segment of flat glass 220. The laser lightsource 40 is mounted such that the linearly polarized light beam 42 willenter one of the shorter sides of the coupling prism 80 at an angle ofapproximately 45 degrees from a plane parallel to the triangular sidesof the coupling prism 80.

This results in the linearly polarized light beam 42 entering the topside of the segment of flat glass 220 at approximately a 40.51 degreeangle with respect to the normal of the segment of flat glass 220 at thepoint of entry. Fluorescent light generated from the light beam 42inside the glass of the segment of flat glass 220 is observed exits tothe other of the shorter sides of the coupling prism 80. The light beam50 has been affected by the stress field within the segment of flatglass 220.

The light beam 50 passes through the quarter wave plate 52 and thepolarization rotator 54. For purposes of convenience in mounting thevarious components of the glass stress measurement apparatus in acompact configuration, the bending prism 82 is used to bend the lightbeam 50 at a 90 degree angle. After passing through the quarter waveplate 52 and the polarization rotator 54, the light beam 50 is bent inthe bending prism 82, and then passes through the long pass filter 58,which is mounted on a lens 84 of the CCD camera 60.

Thus, it will also be appreciated by those skilled in the art that, asis the case with the glass container 30 discussed above, if air couplingis used, the compound angle of entry of 69.29 degrees from the normal tothe surface of the flat glass 220 would be maintained. This angle wouldbe achieved by using angles of 45 and 60 degrees respectively inorthogonal planes normal to the surface of the flat glass 220 similarlyto the example previously discussed with respect to the glass container30. The angle of exit from the flat glass 220 would also be 60 degreesfor air coupling. Curved glass would be evaluated in a similar mannerwith the same angles relative to the normal being used for water or aircoupled operation.

It will thus be appreciated by those skilled in the art that theembodiment shown in FIG. 15 is illustrative of the use of the presentinvention to determine the stress contained within flat glass. Dependingupon the size of the segment of flat glass 220, an X-Y scanningtechnique may be used to measure stress at each of a plurality ofspaced-apart points in a linear progression in a first axis (the Xdirection), with the scanning apparatus then being moved in a secondaxis (the Y Direction) which is orthogonal to the first axis, at whichpoint another scan may be done in the direction of the first axis, withthis process being repeated until the entire segment of flat glass 220has been evaluated.

It may therefore be appreciated from the above detailed description ofthe exemplary embodiments of the present invention that it teaches aglass stress measurement system as well as a related method of measuringthe stress in flat glass or curved glass segments. The glass stressmeasurement system and method of the present invention are adaptable forlarge scale flat glass or curved glass segment manufacturing, and theyare thus capable of high speed measurement of the stress in flat glassor curved glass segments. The glass stress measurement system and methodof the present invention also do not require that the flat glass orcurved glass segments be immersed in liquid during the inspectionprocess, thereby not increasing the handling of the flat glass or curvedglass segments being inspected.

The glass stress measurement system and method of the present inventionproduce highly accurate determinations of the stress in flat glass orcurved glass segments. The glass stress measurement system and method ofthe present invention are also capable of measuring the thickness ofeach of the stress layers in flat glass or curved glass segments. Theglass stress measurement system and method of the present invention arecapable of measuring the wall thickness of the flat glass or curvedglass segments. The glass stress measurement system and method of thepresent invention are capable of quickly and accurately measuring boththe stress in and the thickness of a plurality of positions in the flatglass or curved glass segments.

The glass stress measurement system of the present invention is of aconstruction which is both durable and long lasting, and it should alsorequire little or no maintenance to be provided by the user throughoutits operating lifetime. The glass stress measurement system of thepresent invention is also be of relatively inexpensive construction toenhance its market appeal and to thereby afford it the broadest possiblemarket. Finally, the glass stress measurement system and method of thepresent invention achieves all of the aforesaid advantages andobjectives without incurring any substantial relative disadvantage.

Although the foregoing description of the glass stress measurementsystem and method of the present invention has been shown and describedwith reference to particular embodiments and applications thereof, ithas been presented for purposes of illustration and description and isnot intended to be exhaustive or to limit the invention to theparticular embodiments and applications disclosed. It will be apparentto those having ordinary skill in the art that a number of changes,modifications, variations, or alterations to the invention as describedherein may be made, none of which depart from the spirit or scope of theglass stress measurement system and method of the present invention. Theparticular embodiments and applications were chosen and described toprovide the best illustration of the principles of the invention and itspractical application to thereby enable one of ordinary skill in the artto utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. All suchchanges, modifications, variations, and alterations should therefore beseen as being within the scope of the glass stress measurement systemand method of the present invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

1. An apparatus for measuring stress in a segment of glass, comprising:a light beam source that generates a light beam; light beam couplingapparatus for directing said light beam at the side of a segment ofglass at an angle facilitating entry of said light beam into and throughthe side of the segment of glass, said light beam causing fluorescentlight to be emitted within the segment of glass in response to saidlight beam within the side of the segment of glass; fluorescent lightcoupling apparatus for coupling a portion of said fluorescent lightemitted in response to said light beam within the segment of glassoutwardly from the side of the segment of glass; and fluorescent lightprocessing and analysis apparatus that processes the fluorescent lightexiting the side of the segment of glass and determines the stress inthe segment of glass from the processed fluorescent light exiting theside of the segment of glass.
 2. As apparatus as defined in claim 1,wherein said light beam source comprises: a laser that produces a lightbeam which is linearly polarized.
 3. As apparatus as defined in claim 2,wherein said light beam source additionally comprises: polarizationadjustment apparatus which is adjustable to rotate the polarization ofsaid linearly polarized light beam to a desired orientation that willproduce an the largest possible fluorescent light emitted in response tosaid light beam within the segment of glass.
 4. As apparatus as definedin claim 3, wherein said polarization adjustment apparatus comprises:laser mounting apparatus for securing said laser in position, whereinsaid laser mounting apparatus selectively allows said laser to berotated to thereby rotate the polarization of said linearly polarizedlight beam to a desired orientation.
 5. As apparatus as defined in claim3, wherein said polarization adjustment apparatus comprises: a half waveplate located intermediate said laser and said light beam couplingapparatus, said half wave plate being selectively rotatable to therebyrotate the polarization of said linearly polarized light beam to adesired orientation.
 6. As apparatus as defined in claim 1, wherein saidlight beam coupling apparatus and said fluorescent light couplingapparatus collectively comprise: an optical coupling member for locationadjacent the side of the segment of glass, said light beam beingdirected onto said optical coupling member whereupon said opticalcoupling member directs said light beam into the side of the segment ofglass, said fluorescent light emitted from the side of the segment ofglass being collected by said optical coupling member whereupon saidoptical coupling member directs the emitted fluorescent light intofluorescent light processing and analysis apparatus.
 7. As apparatus asdefined in claim 6, wherein said optical coupling member comprises: acoupling prism.
 8. As apparatus as defined in claim 6, wherein saidoptical coupling member is arranged and configured to couple said lightbeam into the segment of glass and to couple said emitted fluorescentlight out of said segment of glass using air as a coupling medium.
 9. Asapparatus as defined in claim 8, wherein said optical coupling member isarranged and configured to couple said light beam into the segment ofglass at a compound angle that comprises an angle of betweenapproximately 40 degrees and approximately 70 degrees from a planenormal to the surface of the glass container at the point of entry, andat an approximately 45 degree angle out of said plane.
 10. As apparatusas defined in claim 9, wherein said optical coupling member is arrangedand configured to couple said light beam into the segment of glass at acompound angle that comprises an angle of between approximately 60degrees from said plane normal to the surface of the glass container atthe point of entry, and at an approximately 45 degree angle out of saidplane.
 11. As apparatus as defined in claim 6, additionally comprising:apparatus for directing a stream of liquid coupling fluid intermediatesaid optical coupling member and the segment of glass to opticallycouple said light beam into the segment of glass and to couple saidemitted fluorescent light out of the segment of glass; wherein saidoptical coupling member is arranged and configured to facilitate thecoupling of said light beam into the segment of glass and to facilitatethe coupling of said emitted fluorescent light out of the segment ofglass.
 12. As apparatus as defined in claim 11, wherein said opticalcoupling member is arranged and configured to couple said light beaminto the segment of glass at a compound angle that comprises an angle ofbetween approximately 40 degrees and approximately 70 degrees from aplane normal to the surface of the segment of glass at the point ofentry, and at an approximately 45 degree angle out of said plane.
 13. Asapparatus as defined in claim 12, wherein said optical coupling memberis arranged and configured to couple said light beam into the segment ofglass at a compound angle that comprises an angle of betweenapproximately 45 degrees from the normal to the surface of the segmentof glass at the point of entry in said plane orthogonal to an axis ofthe glass container, and at an approximately 45 degree angle from saidplane.
 14. As apparatus as defined in claim 1, wherein said fluorescentlight processing and analysis apparatus comprises: fluorescent lightprocessing apparatus that processes said fluorescent light exiting theside of the segment of glass to produce processed fluorescent light; andfluorescent light analysis apparatus that analyzes the processedfluorescent light to derive information indicative of the stress in thesegment of glass.
 15. As apparatus as defined in claim 14, wherein saidfluorescent light processing apparatus comprises: a quarter wave platelocated intermediate said fluorescent light coupling apparatus and saidfluorescent light analysis apparatus to linearly polarize saidfluorescent light exiting the side of the segment of glass, wherein saidquarter wave plate has an axis that is aligned at an angle ofapproximately 45 degrees with respect to a linearly polarized portion ofsaid fluorescent light exiting the side of the segment of glass.
 16. Asapparatus as defined in claim 15, wherein said fluorescent lightprocessing apparatus additionally comprises: an apparatus locatedintermediate said quarter wave plate and said fluorescent light analysisapparatus for generating two images of ideally orthogonal polarizationstates of the linearly polarized portion of said fluorescent lightexiting the side wall of the segment of glass.
 17. As apparatus asdefined in claim 16, wherein said apparatus for generating two imagescomprises: a polarization rotator for alternately modulating thepolarization state of the linearly polarized portion of said fluorescentlight exiting the side of the segment of glass plus and minus 45 degreeswith respect to said axis of said quarter wave plate.
 18. As apparatusas defined in claim 17, wherein said polarization rotator comprises: arotator drive producing alternating positive and negative voltages; anda ferroelectric liquid crystal element that is driven by saidalternating positive and negative voltages from said rotator drive. 19.As apparatus as defined in claim 17, wherein said fluorescent lightanalysis apparatus comprises: a camera for acquiring a first imagethrough said polarization rotator of the modulated linearly polarizedportion of said fluorescent light exiting the side of the segment ofglass at plus 45 degrees with respect to said axis of said quarter waveplate and a second image through said polarization rotator of themodulated linearly polarized portion of said fluorescent light exitingthe side of the segment of glass at minus 45 degrees with respect tosaid axis of said quarter wave plate; and an image differentiator fordifferentiating said first and second images to produce a normalizeddifference image characteristic of the stresses throughout the thicknessof the segment of glass.
 20. As apparatus as defined in claim 19,wherein said fluorescent light analysis apparatus additionallycomprises: an image processor for processing said normalized differenceimage to produce at least one of a retardance curve and a stressparabola for the segment of glass.
 21. As apparatus as defined in claim16, wherein said apparatus for generating two images comprises: apolarizing beam splitter prism having as an input the linearly polarizedportion of said fluorescent light exiting the segment of glass, whereinsaid polarizing beam splitter prism has as outputs said two images ofideally orthogonal polarization states of the linearly polarized portionof said fluorescent light exiting the segment of glass.
 22. As apparatusas defined in claim 21, wherein said fluorescent light analysisapparatus comprises: a pair of cameras for respectively acquiring saidtwo images of ideally orthogonal polarization states of the linearlypolarized portion of said fluorescent light exiting the segment ofglass; and an image differentiator for differentiating said two imagesfrom said pair of cameras to produce a normalized difference imagecharacteristic of the stresses throughout the thickness of the segmentof glass.
 23. As apparatus as defined in claim 22, wherein saidfluorescent light analysis apparatus additionally comprises: an imageprocessor for processing said normalized difference image to produce atleast one of a retardance curve and a stress parabola for the segment ofglass.
 24. As apparatus as defined in claim 14, wherein said fluorescentlight processing apparatus additionally comprises: a filter that passesfluorescent light but not light at the frequency of said light beamsource, said filter being located intermediate the side wall of thesegment of glass and said fluorescent light analysis apparatus.
 25. Asapparatus as defined in claim 24, wherein said filter comprises: one ofthe group consisting of a long pass filter that passes fluorescentlight, a band pass filter that passes fluorescent light, and a notchfilter that passes fluorescent light.
 26. As apparatus as defined inclaim 1, additionally comprising: scanning apparatus for moving saidapparatus for measuring stress in a segment of glass to a plurality ofpositions adjacent different locations on the side of the segment ofglass.
 27. An apparatus for measuring stress in a segment of glass,comprising: a light beam source that generates a linearly polarizedlight beam; light beam coupling apparatus for directing said linearlypolarized light beam at the side of a segment of glass at an anglefacilitating entry of said light beam into and through the side of thesegment of glass, said linearly polarized light beam causing fluorescentlight to be emitted within the segment of glass in response to saidlinearly polarized light beam within the segment of glass; fluorescentlight coupling apparatus for coupling a portion of said fluorescentlight emitted in response to said linearly polarized light beam withinthe segment of glass outwardly from the side of the segment of glass; acamera for acquiring images of the processed fluorescent light exitingthe side of the segment of glass; and fluorescent light analysisapparatus that analyzes the processed fluorescent light to deriveinformation indicative of the stress in the side of the segment ofglass.
 28. An apparatus for measuring stress in a segment of glass,comprising: a light beam source that generates a light beam; light beamcoupling apparatus for directing said light beam at the side of asegment of glass at an angle facilitating entry of said light beam intoand through the side of the segment of glass, said light beam causingfluorescent light to be emitted within the segment of glass in responseto said light beam within the segment of glass; fluorescent lightcoupling apparatus for coupling a portion of said fluorescent lightemitted in response to said light beam within the segment of glassoutwardly from the side of the segment of glass; and fluorescent lightprocessing apparatus that processes the fluorescent light exiting theside of the glass container to determine a stress profile in the side ofthe segment of glass.
 29. A method for measuring stress in a segment ofglass, comprising: directing a light beam at the side of a glasscontainer at an angle facilitating entry of the light beam into andthrough the side of the segment of glass; detecting fluorescent lightemitted in response to the light beam within the segment of glass whichfluorescent light exits the side of the segment of glass; and processingthe fluorescent light exiting the side of the segment of glass andanalyzing the processed fluorescent light exiting the side of thesegment of glass to determine the stress in the segment of glass.